Speed control for industrial trucks or the like



June 7, 1949. c, coc 2,472,646

sPEED CONTROL FOR INDUSTRIAL TRUCKS OR THE LIKE.

Filed July 9, 1945 l l'l lllll l INVENTOR. g CLYDE E.COCHRAN.

Patented June 7, 1949 SPEED CONTROL FOR INDUSTRIAL TRUCKS OR THE LIKEClyde E. Cochran, Cleveland, Ohio, assignor to The Elwell ParkerElectric Company, Cleveland, Ohio, a corporation of Ohio ApplicationJuly 9, 1945, Serial No. 603,977

(Cl. 318F305) Claims.

The present invention relates to industrial trucks and more particularlyto an improvement in the speed control of electrically driven trucks orthe like. More specifically, the present invention relates to a speedcontrol that is an improvement over that disclosed in my United StatesPatent 2,338,097.

In my patent referred to, the industrial truck shown herein had a directcurrent motor having two field windings each having an equal number ofturns. Three distinct speed steps were obtained by the provision of aswitching mechanism having a manually operable speed control memherwhich when moved to the slow speed position would connect the two fieldwindings of the motor in series with one another and also in seriescircuit with a resistance. When the controller member was moved to thesecond speed position the resistance was shorted out and the two fieldlines were maintained connected in series. When the control lever wasshifted to the third speed position, which was the top speed, the twofield windings were placed in parallel circuit relation, and in theprocess of changing the field windings from series to parallel, i. e.,from the second to third speed, the switch mechanism operated to firstdisconnect one-half of the field of the motor, that is, one fieldwinding before the parallel cir cuit relation was established. Thisdisconnection of half of the field had no effect on the speed of themotor, however.

An object of the present invention is to provide a fourth speed step inthe control of industrial trucks of the type described, or the like,which speed steps may be effected by the switching mechanism disclosedin my patent referred to hereinbefore.

Another object of the invention is to provide a driving mechanism for anelectrically driven industrial truck in which the acceleration betweenthe speed steps is substantially uniform.

Still another object of the invention is to provide a driving mechanismfor an electrically driven industrial truck which is controlled by aswitching mechanism, and the arcing and heating of the switchingmechanism is minimized whereby lighter switching parts may be utilizedwithout increasing the heating thereof or the burning contacts.

In carrying out my invention, I provide two although other ratios may beused. In shorting ployed as well.

out the shorter field winding in changing the winding circuits fromseries relation to parallel, only the winding having the greater numberof turns is maintained in the motor in the circuit so that a third speedstep is provided intermediate the second speed and third or top speedfor merly obtained in the system shown in my patent mentionedpreviously. When the switching mechanism is actuated to the fourth speedor top speed, the long and short windings are in parallel circuit, thusincreasing the current in the armature without a corresponding increasein the field so that a fourth and top speed step is thereby providedwithout changing the construction or arrangement of the switchingmechanism.

Other objects and advantages of my invention will be apparent from thefollowing detailed description of a preferred form of embodiment of myinvention, reference being bad to the accompanying drawing wherein- Fig.1 is a side View in elevation of one end of an industrial truckembodying my invention;

Fig. 2 is a diagrammatic illustration of the motor circuit and contactmechanism for the speed control of the truck shown in Fig. 1, thecontact mechanism being shOWn in the off position;

Fig. 3 is a view similar to Fig. 1, but showing the contact mechanism inthe low or first speed position;

Fig. 4.- is a view similar to Fig. 1, but showing the contact mechanismin the second speed position;

Fig. 5 is a View similar to that of Fig. 2, but showing the contactmechanism in the third speed position; and

Fig. 6 is a view similar to Fig. 2, but showing the contact mechanism ina fourth or top speed position.

Referring now to the drawings, I have shown an industrial truck it thatis adapted to be driven by a series wound, direct current motor which isdriven by current from a suitable storage battery, although any othersuitable source could be em- The motor includes an armature l2 and twofield windings l3 and I l. Preferably, the armature is wave wound, andthe field winding l3, for example, has a fewer number of turns than thefield winding 54. Also opposite poles are Wound with an equal number ofturns, but the poles of the opposite field will have an unequal totalnumber of turns. It is to be understood that the number of turns in thewindings may be varied somewhat, but in the present embodiment of theinvention, I prefer that the winding l3 consist of 24 turns and that thewinding l4 consist of 49 turns. With an 18-cell lead battery a verydesirable and uniform range of speeds may be obtained. Other ratios havebeen employed, however, such as 19 /2 turns to 41 turns, and 16 turns to49 turns. The armature is preferably wave wound so that there will be noundesirable effect of unbalanced flux values, and as opposite poles areexcited by equal turns there is no mechanical unbalanced effect.

The direction and speed of the motor for the truck l may be controlledby the operator by switching mechanism indicated generally at it, whichmechanism includes a speed" control l9 and a reverse lever Ell. Theswitchingmech'anism' H! is fully disclosed in my patent referred tohereinbefore, and it is unnecessary todescribe the details thereof atthis time.

Referring to Fig, 2, the circuit for the motor, including the switchingmechanism i8, is shown diagrammatically to illustrate the motor circuitwhen the speed control lever l-9 is-moved tothe off position and thereverse lever 2i) is moved to the neutral position. The contacts St, S2,St, St and S5 are adapted to be actuated by the speed control lever l9and the two sets of contacts F and R are adapted to be actuated by thereverse lever 20, the contacts F bein closed when the lever 20 is movedto the forward position and the contacts B when the lever ismoved toreverse position. It will be noted that when lever i 8 is moved tothebff" position all contacts The motor control circuitmoved to thereverse-position for closing contacts a B. When this occurs the circuitindicated in heavy lines will be established: and the motor will act asa generator and the current so generated is dissipated by the resistanceRI. If the truck is rolling in the opposite direction, its speed may bechecked in a similar manner by throwing lever 59 to the off position andmoving lever 2t to the forward position.

Referring to Figs. 3 to 6, the circuits for effecting four differentsteps of speeds of the motor are illustrated diagrammatically; Referringto Fig. 3, the motor circuit is shown-whenthe speed control lever ismoved to the first speed step and the reverse lever 20 is moved to theforward position. The heavy lines indicate the path of the current andit will be observed-thatthe windings l3 and M are connected in seriescircuit relation and they are also connected in series withsuitableresistance RZ so that a relatively low speed is obtained.

Referring to-Fig. 4, the motor circuit is shown when the speed controllever I9 is moved to the second speed position and the lever 20 set forforward speed. The heavy lines indicate the circuit, and it will benoted that the resistance R2 is shunted or short circuited by theclosure of contacts S t and that the windings l3 and I i are retained inseries circuit. The omission of R! from the circuit increases thecurrent in the notor with a consequent increase in speed.

Referring to Fig. 5, the motor circuit is shown when the speed controllever is moved to the third speed position and reverse l'eve'r 253 is inthe forward position. It will be noted that winding i3 is disconnectedfrom circuit by the opening 4 of contact SI and that the field winding Malone is in series with the armature l2. This produces a third speedwhich is slightly greater than the second speed as the resistance ofcoil 13 is removed and also the flux density of the field is decreased.

Referring to Fig. 6, the'circuit for the motor is showndiagrammatically'to illustrate the circuit when the speed control leveris is moved to the fourth or top speed position while the reverse leveris in the forward position. It will be'observed that the windings l3 andi l are now connected in parallel circuit with one another and in serieswith the" armature l2, and by this circuit the energization of thearmature is increased without a corresponding increase in the fillX ofthe held so that a distinct fourth increase in speed is obtained.

Tests'have shown that a loaded truck in which the coils l3 and I4 have24% to 49 turns, respectively, the speed of the truckin the first speedposition will be approximately -1.9 miles per hour; in the second speedposition a speed of-3.2= miles per hour; the third speed, a speed of 3.7and in the fourth speed a speed of 4.4 miles per hour. The same truckwith no load at the speeds of 3.1 or first speed; 4 miles perhourfor'thesecond speed; 4.8 miles per hour for the third speed and 5.5miles per hour for the fourth speed. It will be observed that the speedsteps thus obtained are substantially uniform-and that the speeds aresuch as to be desirable for use in congested areas and that the operatoris provided with a maximum range of speeds, each step of speed havingapproximately the same difference over adjacent steps.

It is to be understood that the same; speed steps may be had when thelever" t9" is moved to the reverse position, the only difference beingin the change of direction of the flow of current through the motorcircuit-s. It will be apparent that by my invention, I- have provided anovel speed control for an electrically driverrindustrial truck in whichgreater flexibility in operation of the truck may be had by theprovision of a greater range of speed steps. This increased speed rangeis obtained by a relatively simple expediency and requires noadditional-control equipment over that described in my aforementionedpatent.

Although I have described a preferred form of embodiment of my invention,fit is. to be understood thatthe invention maybe embodied in otherforms, all of which fall withinthe scope of the claims which follow.

I claim:

1. In an industrial truck or the like-,driVing mechanism for said truckincluding'ia' series wound electric motor having. two" field: windings,one of said windings having a substantially greater number of turns thanthe other of said windings; a source of electric "energy for said motor;and means for controlling" the speed of the motor, said means includinga manually operable control member, and being operable to consecutivelyconnect said windings in series, to render one of said windings onlyeffective and then to connect said windings in parallelxas said; controlmember is moved consecutively through three speed control positions.

In an industrial. truck. or the like, driving mechanism for said truckincluding-aseries wound electric motor having two field windings, one ofsaid windings having a substantially: greater number of turns than theother-of said'windings;

a source of electric energy for said motor; and means for controllingthe speed of the motor, said means including a manually operable controlmember and being operable to consecutively connect said windings inseries, to render said one winding only effective and then to connectsaid windings in parallel as said control member is moved consecutivelythrough three speed control positions.

3. In an industrial truck or the like, driving mechanism for said truckincluding a series wound electric motor having two field windings, oneof said windings having a substantially greater number of turns than theother of said windings, the ratio of turns of said windings beingapproximately forty-nine to twenty-four and one-half; a source ofelectric energy for said motor; and means for controlling the speed ofthe motor, said means including a manually operable control member andbeing operable to consecutively connect said windings in series, torender one of said windings only effective and then to connect saidwindings in parallel as said control member is moved consecutivelythrough three speed control positions.

4. In an industrial truck or the like, driving mechanism for said truckincluding a series wound electric motor having two field windings, saidwindings being disposed on two opposite poles, each pole having an equalnumber of turns thereon, one of said windings having a substantiallygreater number of turns than the other of said windings; a source ofelectric energy for said motor; and means for controlling the speed ofthe motor, said means including a manually operable control member andbeing operable to consecutively connect said windings in series, torender one of said windings only effective and then to connect saidwindings in parallel as said control member is moved consecutivelythrough three speed control positions.

5. In an industrial truck or the like, driving mechanism for said truckincluding a series wound electric motor having two field windings, oneof said windings having a substantially greater number of turns than theother of said windings, a source of electric energy for the motor; andmeans for controlling the speed of the motor, said means including amanually operable control member, and being operable to consecutivelyconnect said windings in series, to render the longer of said windingsonly efiective and then to connect said windings in parallel as saidcontrol member is moved consecutively through three-speed controlposition.

CLYDE E. COCHRAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,996,476 Krause Apr. 2, 19352,338,097 Cochran Jan. 4, 1944

